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Патент USA US3038741

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June 12, 1962
N. MILLERON
3,038,731
VACUUM SEALING MEANS FOR LOW VACUUM PRESSURE-S
Filed March 14, 1958
>
_
2 Sheets-Sheet 1
FIG. I.
INVENTOR.
NORMAN M/LL ERON
BY
A TTORNE)’.
June 12, 1962
N. MILLERON
3,038,731
VACUUM SEALING MEANS FOR LOW VACUUM PRESSURES
Filed March 14, 1958
2 Sheets-Sheet 2
7
7
7
I24
r24
32
20]
FIG. 2.
FIG. 3.
62
571
WEV/
42/
r/ »/1
[40
43
FIG. 4.
INVENTOR.
FIG. 5.
BY
NORMAN M/LLERON
%M/4T QMW
ATTORNEX
United States Patent 0 ”
3,038,731
Patented June 12, 1962
1
2
3,038,731
ingly, these sealants and structural materials may be
employed in the construction of many different types of
VACUUM SEALING MEANS FOR LOW
VACUUM PRESSURES
Norman Milleron, Berkeley, Calif., assignor to the United
States of America as represented by the United States
Atomic Energy Commission
Filed Mar. 14, 1958, Ser. No. 721,615
3 Claims. (Cl. 277-22)
scaled closures as well as in other sealed mechanism as
hereinafter described. The invention is easily adaptable
to any vacuum closure and to the sealing of valves and
translatable or rotary devices where the moderate toler
ances herein speci?ed are provided. Both heat and elec
tricity can be conducted through the seals and lubrica
tion of contacting parts is also provided by the sealants.
This invention relates in general to vacuum seals and 10
Accordingly, an object of the invention is to provide a
methods for producing same and more speci?cally to seals
means of effecting vacuum seals.
affected by the surface tension of a thin layer of liquid
Another object of the invention is to provide vacuum
metal of low vapor pressure, under critical conditions.
seals between two surfaces over pressure differentials as
In high vacuum technology such as mass spectroscopy,
great as 10—8 mm. Hg and at temperatures up to at
particle acceleration, controlled thermonuclear reactions
and others, various manipulations, motion transmitting
and closure operations must be performed in vacuum
pressures in the region lower than 10'5 mm. Hg. Exist
ing vacuum technology, however, provides only partially
satisfactory equipment for attaining and maintaining such
least as high as 500° C.
Still another object of the invention is to provide a
method of sealing gaps between stationary or movable
surfaces with liquid metal sealants held in position there
between by wetting and surface tension.
A further object of the invention is to employ metal
20
High vacuum valves and movement
alloy sealants having melting points below 100° 0, low
transmitting seals are generally dependent upon organic
sealants and lubricants, all of which generally have vapor
vapor pressures and high surface tension in sealing gaps
reduced pressures.
between stationary or movable surfaces of a vacuum
pressures precluding their use at pressures in the region
system.
of 10-6 mm. Hg, particularly at the elevated tempera 25
A still further object of the invention is to provide
tures necessary for degassing of chamber walls. With
apparatus for use in vacuum systems in which a liquid
large closures, e.g., in tanks housing particle accelerators,
metal sealant is used to effect the vacuum seal.
it is frequently necessary to employ surface-to-surface
Other objects and advantages will become apparent by
deformation ?ts, sometimes using a machined deformable
consideration of the following description and accompany
copper gasket. Inordinately large closing forces are neces 30 ing drawing of which:
1
sary and the surfaces and gasket materials cannot be re
FIGURE 1 is a vertical cross-sectional view of an
used after deformation. Entirely satisfactory seals have
evacuated chamber having a closure sealed with a liquid
heretofore been obtained only by permanent and semi
metal;
permanent joining methods, such as welding, hard solder~
FIGURE 2 is a vertical cross-sectional view of a ?anged
ing, wetting with glass, etc., where there is sealing con 00 CI joint having machined ?ange surfaces which are sealed
tact between materials on a truly molecular scale.
with a liquid metal;
It has been discovered that certain liquid metals, and
FIGURE 3 is a vertical cross-sectional view of a
especially certain alloys, formed of metals having vapor
?anged joint in which opposing ?ange surfaces are sealed
pressures of below about 10"8 mm. Hg at about 350° C.
with a deformed metal compression gasket employed in
to 500° C. and above, and melting points below 100° C. 40 conjunction with a liquid metal;
may be used to seal closures or other closely ?tted sur
faces in vacuums of 10'8 mm. Hg or lower and at tem
peratures at least as high as 500° C. This is accomplished
by utilizing the surface tension forces of the sealant
metal which is applied in such a manner that true molecu
lar wetting of the speci?ed closure surfaces is achieved.
The surfaces to be sealed must be disposed in proximity
with opposing faces being spaced within a maximum dis
FIGURE 4 is a vertical cross-sectional view of a glass
window retained at the end of an evacuated machined
metal tube by atmospheric air pressure and sealed thereto
with a liquid metal;
FIGURE 5 is a vertical cross-sectional View of a re
motely controlled vacuum valve having a closure sealed
with a liquid metal; and
FIGURE 6_ is a vertical cross-sectional view of a ro
tance which distance is of the order of one-thousandth of
tatable shaft sealed with a liquid metal.
a centimeter for atmospheric pressure differences and 50
The surfaces to be vacuum sealed in accordance with
correspondingly larger for lower pressure differentials.
the invention are constructed from the class of materials
Alloy mixtures of gallium, indium and tin yield best re
sults and therefore are preferred. In addition to gallium,
indium and tin only lead and bismuth have been found to
speci?ed hereinafter and arranged in contiguity in the
various types of apparatus joints contemplated herein.
Moreover, characteristically, in speci?c embodiments, at
possess the requisite properties for formulating such seal 55 least one side of the sealed joint will be exposed to a
ants, especially in alloy form, and gallium must generally
high vacuum and at least intermittent elevated tempera
be present to produce best results. All metal and siliceous
materials of construction are in general wet by these seal
ants. Exceptional wetting may be obtained with surfaces
ture conditions.
In other instances a pressure differen
tial ranging upwards to at least atmospheric pressure will
exist across the sealed joint. Generally speaking, such
formed of the metals stainless steel, brass, copper, nickel, 60 jointed apparatus is sealed by disposing certain liquid
molybdenum, tantalum, and tungsten and with the sili
or molten metals between said contiguous surfaces as a
ceous materials, glass, including Pyrex, quartz, and syn
sealant.
As an initial operation in producing the seal any
thetic mica, all of which materials are frequently used
as materials of construction for high vacuum systems
grease or other gross impurity is removed from the seal
wherein high temperatures may be employed. Accord 65 surfaces, e.g., with an organic solvent, and the general
3,038,731
0
4
seal areas are separately delineated. The extent of
the seal areas to be wetted determines the amount of
metal applied on the opposing surfaces in order to ob
tain a ?lm of the desired thickness. Conventional meth
more conveniently employed and those which melt be
low about 60° C. and especially those approximating
eutectics, i.e., having melting points within about 15° C.
ods may be employed to effect such wetting; however,
ultrasonic soldering or wetting techniques are preferred
and the somewhat higher melting alloys are liquids at
of the eutectic temperature, are preferred.
Gallium
temperatures occurring
many operating vacuum sys
tems so that auxiliary heating is not required. How
ever, in rigorous outgassing procedures carried out at
ultrasonic method, the metal surface is usually disposed
high temperatures all of the indicated materials are
horizontally and the sealant metal in a solid or liquid
form is applied to the delineated surface of the joint, 10 liquid and provide effective sealing when applied in ac
cordance with the invention.
which is heated to a temperature above the melting
point of the sealant metal, and wetting is accomplished
TABLE I
by applying ultrasonic energy. Other techniques, e.ig.,
dipping may be used. Certain of the liquid metals will
Vapor pressure
Surface tension
be found to readily wet the joint surface, requiring no 15 Metal alloy, percent) Mclting
Wt.
point,
further treatment. The amount of metal applied is that
° C
mm. Hg
° C.
dynes/
° 0.
required which on mating the joint surface occupies the
cm.
since extraneous material is not added.
In using the
space therebetween at least along a line around the area
of contact or as a band across the gap area of the joint
and normal to the direction of the pressure which will 20
exist when the seal is placed in use. The joint is, of
course established while the sealant metal is still liquid,
i.e., molten. More particularly, the opposing joint sur
Gallium _______________ __
29. 9
l0- 8
500
735 to
‘10
__
156. 4
l0- 3
500
340
250
Bismuth
Tin ____________________
__
_.
-_
271.
231. 09
i0- K8
10-
300
500 {
Lead __________________ _-
327. 4
10- 8
350 {
Indium. _ ___
,.
faces are brought into contiguity in any way consistent
62.5 Ga, 21.5 In, 16 sh..
With the shape of the surfaces so that matching wetted 25 62 Ga, 25 In, 13 Sn ____ 69.8 Ga, 17.6 In, 12.5 Sn.
parts contact each other. The two ?lms merge without
76 Ga, 24 In ___________ ._
additional closing force other than that necessary to
92 Ga, 8 Sn ...... ._
___
bring the surfaces within the aforementioned clearance,
generally one-thousandth of a centimeter where atmos
pheric pressure is to be retained.
With proper design
and workmanship closure and sealing may be most con
veniently effected merely by application of a vacuum
pressure differential. Once the seal is effected the tem
perature of the liquid metal may be allowed to fall below
the metal melting point without loss of the seal in 35
tegrity. However, in order to obtain extremely low
pressures, i.e., below 10"6 mm. Hg, in the system, bake
out at a higher temperature is necessary in accordance
with conventional vacuum practice.
More speci?cally, molten sealant metals gallium, 40
238
49 Bi, 18 Pb, 12 Sn an
21 In ________________ __
4e Bi, l8 Pb, 15 S11 and
18 In ________________ __
32.7 Bi, 7.5 Pb, 16.7 Sn,
and 43.1 In __________ ._
49.5 Bi. 17.6 Pb, 11.6 Sn
and 21.3 In __________ __
TABLE II
Sealants (numbers refer to Wt. percent)
Materials of Construction
Gallium _______________________________ -_
Copper, brass, stainless steel,
nickel, molybdenum, tan
talum, tungsten, glass,
quartz, Pyrex and synthet
thereof, examples of which are shown in Table 1, have
ic mica.
}Molybdenum,
tantalum,
glass, Pyrex andquartz.
been found satisfatcory in practice to wetting and seal
ing surfaces formed of stainless steel, brass, copper,
nickel, molybdenum, tantalum, tungsten, and siliceous
Copper, brass, stainless steel,
nickel, molybdenum, tan~
talurn, tungsten, glass,
quartz, Pyrex, synthetic
materials, particularly glass, (including Pyrex) quartz
instances, except for the temperature exceptions noted
1%
~70 Ga, ~30 Sn _______ -.
indium, tin, bismuth, lead, and alloy combinations
and synthetic mica as indicated in Table H. Due to
the diverse nature of such materials other materials of
construction should prove to behave similarly. The
indicated materials may ‘be used to construct sealed
joints capable of withstanding vacuum pressures of at
least 10“8 mm. Hg at 350° to 500° C. and above in all
28g
mica.
' Brass, copper, stainless steel
and nickel.
General principles and basic considerations relevant
to the construction and operation of liquid metal sealed
vacuum apparatus in accordance with the invention will
immediately hereinafter, and as low as 10*10 mm. Hg
in the case of molybdenum and a few of the other 55 now be set forth with reference to FIGURE 1 of the
drawing as illustrated therein. A vacuum chamber 10
metals. Generally speaking, the metals tantalum, tung
including a housing 11 having an open end closed with
sten and molybdenum do not undergo undesirable chem
an overlapping cover plate 12 is disposed contiguously in
ical reactions or loss of the sealant as by diffusion into
near contact position with the plantar edge surface 13 of
the surface vbelow temperatures of about 500° C. in
the side walls of the housing 11 constructed of materials
vacuo. The non-metals de-wet at 300° C. and stainless
speci?ed above. Vacuum conduit 14 couples chamber 10
steel cannot be used above 250” C. Brass, Cu and Ni
to a vacuum pump (not shown) capable of evacuating
form alloys at appreciable rates above room tempera
the chamber to a very high vacuum level. A liquid seal
tures. Gallium is stable to at least 150° C. in air and
ant metal or alloy of the character described is disposed
the remainder are stable to at least 250° C. in air. The
in wetted adherent relation between the edge 13 of the
metals lead and bismuth have vapor pressures some
housing 11 ‘and corresponding surface of the cover plate
what higher than 10*8 mm. Hg above 350° C.
The lower melting alloys containing gallium and ap
proximating eutectic mixtures are obviously most de
sirable since they are liquids at usual ambient tempera
as a continuous ribbon 16.
When a sealant metal is em
ployed which is solid at the ambient temperature elec
trical resistance heaters 17 may be attached to the cham
70 ber walls \and cover plate to maintain the temperature at a
level ‘at which the metal is liquid, when required. In uti
lizing apparatus sealed in accordance with the invention
tendency to supcrcool and they are therefore found to
other heating means including ovens, radiant heat, induc
tures. The gallium, indium, tin ternary eutectic melts
at about 107° C.; however, such alloys have a strong
remain liquid to lower temperatures in practice.
The
liquid metals or alloys which melt below 100“ C. are
tion heating, etc., may also be employed.
Upon application of the vacuum with the temperature,
an
3,038,731
6
5
maintained above the melting point, the liquid metal seal~
ant 16 is distended inwards as indicated in FIGURE 1.
The exact distance to which the surfaces may be sepa
rated without disrupting the liquid metal surface tension
seal may be calculated by considering the mathematical
relationships governing the behavior of the liquid metal
supported by surface tension and wetting the gap (D)
between housing edge and cover plate surfaces as shown
in FIGURE 1. Complete wetting of the surfaces implies
zero contact angle between the solid and liquid surfaces,
Modi?cation of the foregoing ?anged joint 20 to in
clude a deformable copper or other metal gasket 31 inter
posed between the ?anges ‘22 and 23 yields ?anged joint
30 shown in FIGURE 3. In order to preserve the ?ange
surfaces at the expense of the deformable gasket and to
obtain higher vacuums a liquid metal sealant 32 is dis
posed so as to wet gasket 31 as well as adjacent surfaces
22 and 23.
In FIGURE 4 there is illustrated an assembly 40' where
in a glass disc 41 employed as a closure for tubular con
which merely means that the adhesion between the solid
duit 42 also made of glass or another of the indicated
and liquid is greater than the cohesion in the liquid.
construction materials is sealed by application of a liquid
Then, with a vacuum pressure differential applied across
metal sealant 43‘ between contact surfaces. No closure
pressure other than the pressure differential which exists
the liquid, the liquid is subjected to a force directed in
wardly toward the lower pressure side. However, for
small ‘gaps continuously and adequately wetted by liquids
with su?iciently high surface tension, the surface tension
effectively resists absorption and passage of the gas. The
mathematical expression which relates the maximum pres
sure difference which can be withstood across a curved
liquid surface to the relevant physical properties is as
follows:
1
on evacuation is necessary even in a vertical position.
The glass must ordinarily be polished or lightly ?re
polished before proper wetting can be achieved, as by
ultrasonic methods.
A liquid metal sealed vacuum valve 50 is shown in
FIGURE 5, wherein there is provided a generally cylin
drical valve body 51 provided with lower and side ?anged
couplings 52 and 53, respectively. Interiorly, the valve
body 51 is provided with a circumferential shoulder 54
which serves as a valve seat and is enlarged inwardly of
said seat to accommodate a closure disc 56 which is ar
where
ranged to provide horizontal movement and seating con
tact against said shoulder 54. More particularly, the disc
56 is supported by a push rod 57 attached to the side wall
P1 is ‘atmospheric pressure in the limiting case.
the side wall portion of body 51 in a vacuum tight ar—
thereof and extending outwardly through a perforation in
P2 is vacuum pressure.
7 is the coe?icient of surface tension of the sealant.
R1 is the radius of curvature of the sealant on the pres
surized side.
R2 is the radius of curvature taken orthogonally to R1,
and corresponds to the curvature of the ribbon of metal
along the wetted surface.
In usual practice the most extreme situation exists
where P1 is atmospheric pressure since with lower pres
sure differentials less disrupting force is present. For all
practical situations vP2 is negligible and R1 is a great deal
less than R2, so that the above expression simpli?es to:
Play/R1. The limiting distance, D, between the seal
surfaces is the quantity 2R1, wherefore the distance D,
the absolute distension pressure P1, and the coe?icient of
rangement provided by \Sylphon bellows 58 attached to the
rod 57 and exterior of the body 51. A bracket 59 slid
ably engaging the pushrod 57 and attached to the in
terior of body 51 allows horizontal movement of the disc
56 on actuation of external portions of the pushrod 57
and guides the disc into accurately seating contact with
shoulder ‘54. A liquid metal sealant 61 is applied to the
areas of contact between the disc 56 and shoulder 54.
Heating means in the form of an electrical resistance heat
ing element 62 attached to exterior surfaces of body 51
may be employed to provide heat by conduction to main
tain the sealant metal in liquid condition during use.
A rotatable shaft seal arrangement 70 employing a
liquid metal sealant is illustrated in FIGURE 6 of the
drawing as constructed in a fragmentary wall portion 71
of a typical high vacuum system (not shown). The wall
71 may be made of usual materials such as carbon steel
or the like for economy; however, to meet the require
ments of the invention a preferred material such as stain
atmospheric pressure is ~106 dynes/cmF, the limiting dis 50 less steel or molybdenum or tantalum for high vacuum
surface tension 7 are directly inter-related as indicated by
Illustratively for a sealant metal with a
surface tension of 500 dynes/cm. in instances where the
' the equations.
tance, D, to which the surfaces may be separated is lim
ited to a maximum of about one-thousandth of a centi
meter. While exact distances may be calculated for each
metal of a different surface tension, the aforementioned
distance of one-thousandth of a centimeter may be used
as a practical working limit for atmospheric pressure
differential and with the vacuum pressures and tempera
tures normally encountered, i.e., 10-8 mm. Hg at 500°
C., as in outgassing operations, etc. With lower pressure
high temperature bakeout (outgassing) is required. Ac
cordingly, an enlarged perforation is provided in wall 71
and a ?anged journal 72 formed of a preferred metal is
?tted and secured therein as by heliarc welding of the
peripheral rim 73 of the journal ?ange to adjacent inner
surfaces of the body 71. A rotatable shaft 74, provided
with a bearing collar of bushing 76 of one of said pre
ferred metals secured in vacuum-tight relation thereon as
by heli-arc welding of the inner edge 77 to the shaft is dis
differentials and lower temperatures correlatively larger 60 posed in the journal 72, to extend from an actuated device
within the system (not shown) outwardly from wall 71.
gap tolerances are permitted.
'
A liquid metal sealant 78, of the character described, is
Application of the foregoing principles in the sealing
disposed between the bearing bushing 76 and bearing sur
of compression ?tted ?anged joint 20 shown in FIGURE
face 79 of the journal 72.
2 is effected by disposing a liquid metal sealant 21 to wet
In the event that the sealed shaft is to be employed as
continuous circumferential portions of ‘the abutting sur 65
hereinbefore described a close tolerance is required to
faces of ?anges 22 and 23 of the joint, whereby the liquid
withstand disruptiton of the sealant by an atmospheric air
metal is supported by surface tension therebetween. In
pressure gradient as indicated above. However, such
ordinary vacuum practice such surfaces must be carefully
close tolerance requirement can be avoided by providing
machined to as close a tolerance as possible and there
after closed as by ?ange bolts 24 or other closing means 70 a greater clearance, e.g., 0.0105 in. between the bushing
and journal maintained by supported alignment of the
to a deformation fit in order to ‘achieve reasonable vacuum
shaft. This larger tolerance is made possible by applica
integrity. In extreme cases such joints cannot be used
more than once because of deformation. However, utili
tion of a gross vacuum to the outer portion of the sealed
zation of the liquid metal sealant eliminates the need for
area.
both close machining and deformation ?tting.
More particularly, a cylindrically chambered cap 81,
8
evacuated to less than 10 mm. Hg through conduit 82.,
thereof, as speci?ed in Table II, were applied to each of
may be secured to the wall 71 by machine screws 83 with
the surfaces and wetted as described hereinbefore. The
?anged surfaces were bolted down to within the tolerance
required for each of the metal sealants used, separate
the ?anged portion 84 sealed in vacuum-tight relation by
means of O-ring 86 disposed in groove 87. Ball bearings
88 disposed in spaced relation Within the chambered por
Cl
trials being run both with and Without deformable Wetted
tion of cap 81 engage the shaft 74 to provide the above
metal gaskets constructed of materials similar to each
indicated support and alignment. Outwardly projecting
particular joint. Vacuum pressures at least as low as 10"’!
portions of the shaft 74 are sealed by an O-ring 89 dis
mm. Hg, and in some cases as low as 104°, were created
posed in the chambered portion 91 of a perforation pro
on the interior of each pair of ?anged joints. Leak tests
vided centrally in the end wall 92 and retained therein 10 were made with a standard helium. leak detector. Tem
by a collar 93 secured by machine screws 94.
The rotatable shaft seal 70 may be modi?ed to provide
perature cycles were run successfully as high as at least
500° C., except in the case of stainless steel, where fail
rectilinear motion of shaft 74 by disposing sealant along
ure occurred at 250° C., and in the case of brass, copper
an extended length of the shaft and substituting rectilinear
and nickel, which were used only at room temperature,
motion bearings for ball bearings 88. Heating means 15 and in the case of the non-metals where non-wetting oc
may be provided as described above.
curred at about 300° C. Uniformly good results were
obtained.
While the invention has been disclosed with respect to
several preferred embodiments, it will be apparent to
amples.
20 those skilled in the art that numerous variations and modi~
Example I
?cations may be made within the spirit and scope of the
invention and thus it is not intended to limit the invention
The ends of rigid cylindrical tubes of 3%: in. diameter
except as de?ned in the following claims.
closed with rigid discs of l in. diameter were sealed with
What is claimed is:
liquid Ga-In-Sn alloy sealant. Stainless steel, quartz and
1. High vacuum apparatus including in combination
Pyrex were used in all possible combinations of tubes
mating contiguous surfaces composed of materials se
and discs. Tight seals were achieved by insuring that con
lected from the group consisting of copper, brass, stain
tact surfaces were within 10“3 cm. gap tolerance, were
less
steel, nickel, molybdenum, tungsten, tantalum, glass,
lightly ?re-polished (in the case of glass) and were com
quartz and synthetic mica disposed to expose the area
pletely wetted by the sealant alloy applied by means of
a standard ultrasonic soldering technique. Pressures as 30 of contiguity to a vacuum pressure differential across a
distance, D, means for retaining said surfaces in said con
low as 10-8 mm. Hg were then maintained as measured
tiguous relation and a liquid metal sealant selected from
by a helium leak detector. Temperature cycles as high
the group consisting of the alloys of gallium and tin, the
as 250° C. were also employed without failure.
The further details of the construction and operation of
vacuum apparatus provided with seals in accordance with
the invention will become apparent in the following ex
Example 11
After plastically deforming 0.008 inch thick stainless
alloys of bismuth, lead, tin and indium, the alloys of gal
lium, indium and tin and the alloys of gallium and indium
wetting said contiguous surfaces and being suspended
therebetween, said distance D being not greater than in
steel sheets in a shallow dish by means of a simple rub
dicated by the expression 2'y/P1, where v is the coe?’icient
ber die, they ‘were sealed into a 3 inch diameter stainless
of
the surface tension of the metal sealant selected in
steel tube with molten 50--50 Pb-Sn solder after proper
wetting of tube and disc. The dish-shape was necessary 40 dynes/cm. and P1 is atmospheric pressure, in dynes/cm.2
whereby vacuum pressures at least as low as 10-8 Inm. Hg
to avoid the wrinkle mode of deformation due to expan~
at 250° C. may be maintained.
sion while the joint was being heated to the melting point
2. High vacuum apparatus including in combination
of the solder. Temperatures as high as 350° C. and pres~
sures as low as 10*8 mm. Hg were employed without detection of a leak with a helium leak detector.
Example III
A rotatable shaft of the type shown in FIGURE 6 was
constructed using stainless steel as the journal and shaft
bushing material. Care was taken to avoid contact be
tween the cladding and the bearing. During a 72 hour
test run at a temperature above the liquid metal melting
point a differential pressure of 10‘ mm. helium was main
tained across the seal using liquid Ga, In, Sn eutectic
alloy as sealant. No leak was detected. The difference
in diameters between the shaft and the “bearing” between
which the metal seal was located was 0.010 inch. The
shaft was used to operate a roller which fed wire off a
spool into a vaporization device inside the vacuum shell
by cooperating with a second shaft operating with a simi
lar seal. Continuous positive motion, both forward and
backward, was effected. Speeds were usually less than
10 rpm.
Example IV
mating contiguous surfaces composed of materials se
lected from the group consisting of copper, brass, stain
less steel, nickel, molybdenum, tungsten, tantalum, glass,
quartz and synthetic mica ‘disposed to expose the area of
contiguity to a vacuum pressure differential across a dis—
tance, D, means for retaining said surfaces in said con
tiguous relation, means for heating said surfaces to a tem
perature at least above about 250° C., and a liquid metal
sealant consisting of an alloy of gallium, indium and tin
having a melting point below about 25° C. Wetting said
contiguous surfaces and suspended therebetween, said
distance D not being greater than indicated by the expres
sion 27/P1, where 'y is the coef?cient of the surface ten
sion of the metal sealant selected in \dynes/cm. and P1 is
atmospheric pressure, in dynes/cm.2 whereby vacuum
pressures at least as low as 10—8 mm. Hg may be main
60 tained.
3. High vacuum apparatus including in combination
mating contiguous surfaces composed of molybdenum dis
posed to expose the area of contiguity to a vacuum pres
sure differential across a distance, D, means for retaining
65 said surfaces in said contiguous relation, means ‘for heat
ing said surfaces to a temperature higher than at least
The following experiment was devised to test various
about 250° C., and a liquid metal sealant consisting of
materials of construction and sealants named in Table
62.5 weight percent gallium, 21.5 weight percent indium
II. The list was not intended to be all inclusive, but rather
and 16 percent tin Wetting said contiguous surfaces and
to determine whether the materials tested could be used
in high vacuum work. All of the materials of construc 70 being suspended therebetween, said distance D not being
greater than indicated by the expression 2v/P1, where 'y
tion except glass, Pyrex and quartz were prepared in the
is the coe?icient of the surface tension of the metal seal
form of pairs of ?anged joints the mating faces of which
ant selected in dynes/ cm. and P1 is atmospheric pressure,
were ?at within 0.0001 inch. Glass, quartz and Pyrex
in
dynes/cm?.
were also prepared as ground joints ?tting to within 0.0001
inch tolerance. Various sealant metals, and combinations 75
(References on following page)
8,088,731
10
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Belluzzo _____________ __ Oct. 18, 1908
Rich ________________ __ Ian. 28,
Faber ________________ __ May 4,
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2,771,900
Glesson _____________ .._ Sept. 11, 1945
Mohr et a1. ___________ .._ Oct. 21, 1947
Anderson ____________ .._ Dec. 12, 1950
Carlson et a1. _________ __ May 6,
Smith et a1. __________ -._ Aug. 18,
South et a1. __________ __ Aug. 18,
Leck et a1. ___________ __ Apr. 24,
1952
1953
1953
1956
Kidner _______________ __ July 3, 1956
Dayton ______________ .__ Nov. 27, 1956
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